A simple library for creating CLI REPLs in Dart.


Example Usage:

/// Echoes all entered lines
for (var line in new Repl().run()) {

Statement Validation

By passing a validator to the Repl constructor, you can tell the REPL whether some entered text is a complete statement or not. The REPL calls this whenever a newline is entered to determine whether to yield a complete statement or continue it on a new line. The default validator returns true for all text.

Custom Prompts

By default, the REPL gives no prompt to the user when asking for a statement. You can change this by passing a prompt to the Repl constructor. By default, statement continuations on a new line will start with whitespace equal to the length of the prompt. You can override this by passing in continuation.

See example/example.dart for a demonstration of statement validation and custom prompts.


A history of entered lines is stored. History entries are modified when edited.

By default, a maximum of 50 entries are stored. You can change this by passing maxHistory into the Repl constructor.


  • Left/Ctrl-B: Move left one character
  • Right/Ctrl-F: Move right one character
  • Home/Ctrl-A: Move to start of line
  • End/Ctrl-E: Move to end of line
  • Ctrl-L: Clear the screen
  • Ctrl-D: If there is text, delete the character under the cursor. If there is no text, exit.
  • Ctrl-F: Moves forward one character
  • Ctrl-B: Moves backward one character
  • Ctrl-U: Kill (cut) to start of line
  • Ctrl-K: Kill (cut) to end of line
  • Ctrl-Y: Yank (paste) previously killed text, inserting at cursor
  • Up/Down: Navigate within history

Testing REPLs

If running without a terminal, the input will be printed along with the prompts, allowing you to test REPLs made with this library by comparing stdout to the expected log input and output together.

See test/repl_test.dart for an example of this.

Running on Node

If you compile this to JS with Dart 2, you can run it on Node.

There are a couple of behavior differences:

  • Node's built-in readline library is used, so the supported navigation and history commands may vary from the Dart version.
  • Likewise, line history is managed by Node, and you can't change the maximum number of entries or edit history manually from Dart.
  • Only Repl.runAsync() works. Calling will throw an error.